Searching content-based multimedia data in diverse multimedia environments requires a method of efficiently expressing multimedia contents, and to express diverse data included in a multimedia content, a systematic expression scheme is required.
To fulfill the above requirements, Moving Picture Experts Group (MPEG) 7 defines specifications for descriptors expressing the contents of audio and visual (AV) data, description scheme (DS) defining schema which systematically describes the structure and meaning information of AV data, and Description Definition Language (DDL), which is a language for defining descriptors and description schemes.
The MPEG-7 is related to a structure of metadata for expressing multimedia data such as image, audio, and moving picture.
MPEG-7 query format is a form of a query expressed in MPEG-7 for multimedia data search. MPEG-7 query format defines syntax for searching MPEG-7 documents. In a system for searching MPEG-7 multimedia data, MPEG-7 multimedia data are searched using the MPEG-7 query format.
MPEG-7 query format should be able to exactly express diverse queries from users and diverse query types. For example, there are diverse query types, such as a sentence-type query, e.g., “music video starring Rain”, example-based query using a multimedia file itself as a query, and an MPEG-7 textual description-based query. The above diverse query types should be able to be exactly expressed in MPEG-7 query format. Therefore, it is required to develop a query expression method that can exactly express diverse queries and query types in MPEG-7 query formats for MPEG-7 multimedia data search.
Meanwhile, there is a case where different sub-structures belonging to the same region of an MPEG-7 document are referred to in an MPEG-7 multimedia search. In other words, this is a case that more than one search conditions should be all satisfied within the same region of the MPEG-7 document.
To take an example, to search for an MPEG-7 image file having predetermined length and area at a specific position, a specific position is designated at first and the length and area attributes are designated for the specific location. In short, a secondary search is executed within the result of a primary search.
Therefore, to re-use a pre-designated region in an MPEG-7 multimedia data search, a method of expressing queries by using field types is required. Fields used in the present invention expresses a user query as a query for searching multimedia data. Field types specify the attributes of the fields.
Hereinafter, problems of OutputDescriptionType of a conventional MPEG-7 query format defined as the following Table 1 will be discussed.
TABLE 1<complexType name=“OutputDescriptionType”> <sequence>  <element name=“Field” type=“mp7qf:FieldType” minOccurs=“0”maxOccurs=“unbounded”/> </sequence> <attribute name=“maxPageEntries” type=“positiveInteger” use=“optional”/> <attribute name=“maxItemCount” type=“positiveInteger” use=“optional”/> <attribute name=“freeTextUse” type=“boolean” use=“optional”/> <attribute name=“resourceUse” type=“boolean” use=“optional”/> <attribute name=“outputNameSpace” type=“anyURI” use=“required”/></complexType><complexType name=“FieldType”> <simpleContent>  <extension base=“mpeg7:xPathRefType”>   <attribute name=“typeName” type=“string” use=“optional”/>  </extension> </simpleContent></complexType>
The OutputDescriptionType is a type of an OutputDescription field indicating an output query result. According to the conventional technology, the OutputDescriptionType cannot express an operation result related to a plurality fields as output. FieldType included in the OutputDescriptionType refers to a specific element or attribute. However, since the FieldType is based on XPath, there are some restrictions in expressing a relationship between element and attribute. Herein, eXtensible Markup Language (XML) Path Language (XPath) is a standard of World Wide Web Consortium (W3C) and it is a language describing a method of arraying and processing elements by using a syntax designated on a path based on a structure of an XML document. XPath uses pass expression to define nodes of an XML document. Besides, it uses mathematics, functions and other extensible expressions.
For example, it is not guaranteed that two XPath expressions //Member/Name/GivenName and //Member/Name/FamilyName extract a given name and a family name of the same member from a document presented in Table 2.
TABLE 2<Creator> <Role href=“urn:mpeg:mpeg7:cs:RoleCS:2001:ARTIST”/> <Agent type=“PersonGroupType”>  <Member>   <Name>    <GivenName>Mick</GivenName>    <FamilyName>Jagger</FamilyName>   </Name>  </Member>  <Member>   <Name>    <GivenName>Keith</GivenName>    <FamilyName>Richard</FamilyName>   </Name>  </Member>  <Member>...</Member>  ... </Agent></Creator>
That is, when a query is expressed with the two XPath expressions //Member/Name/GivenName and //Member/Name/FamilyName, a person whose given name is Mick is extracted and a person whose family name is Jagger can be extracted. However, there is no guarantee that a person whose given name and family name is Mick Jagger is extracted.
As describe above, it is required to develop a query expression apparatus and method that can exactly express diverse queries and diverse query types in an MPEG-7 query format and re-use pre-designated region for MPEG-7 multimedia data search.